1. Technical Field
The present invention relates to wireless communications, and more particularly, to a method of transmitting control information in a wireless communication system.
2. Related Art
Today, wireless communication systems have been evolving from the early voice-oriented services into high-speed, high-quality wireless data packet communication systems for providing data services and multimedia services. Moreover, for next generation wireless communication systems, standardization is in progress for high-speed, high quality wireless data packet services. High speed downlink packet access (HSDPA) represents an evolution of the existing asynchronous international mobile telecommunications (IMT)-2000 standard and is an access scheme which is additionally provided for high-speed downlink data transmission. The HSDPA is classified into a frequency division duplex (FDD) HSDPA and a time division duplex (TDD) HSDPA. The TDD HSDPA can support a chip rate of 3.84 million chips per second (Mcps) or 1.28 Mcps. In the TDD HSDPA, uplink and/or downlink resources can be asymmetrically allocated. Thus, when downlink channels are allocated to the maximum extent possible, transmission can be achieved in a most efficient manner with the introduction of the HSDPA.
The HSDPA includes adaptive modulation and coding (AMC), hybrid automatic repeat request (HARQ), etc. The HARQ is a combination of automatic repeat request (ARQ) and channel coding of a physical layer. In the HARQ, a user equipment (UE) receives packet data from a base station (BS) and then informs the BS of whether the data is successfully received or not, so that the BS retransmits the packet data when necessary. According to the HARQ, original packet data is combined with the retransmitted packet data by using at least one of chase combining, full incremental redundancy, and partial incremental redundancy, thereby improving decoding performance. In the chase combining, the retransmitted packet data is the same as the original packet data. In the full incremental redundancy and the partial incremental redundancy, the retransmitted packet data is different from the original packet data. In particular, in the partial incremental redundancy, packet data that cannot be self-decoded is retransmitted.
A high speed downlink shared channel (HS-DSCH) is a downlink transport channel for supporting the HSDPA. The HS-DSCH is associated with at least one high speed shared control channel (HS-SCCH) which is a “shared control channel for HS-DSCH”. The HS-SCCH is a downlink physical channel for carrying upper-layer control information for the HS-DSCH.
A high speed shared information channel (HS-SICH), which is a “shared information channel for HS-DSCH”, is an uplink physical channel for carrying an acknowledgment (ACK)/negative-acknowledgment (NACK) signal. The ACK/NACK signal is used when the UE informs the BS of whether packet data transmitted on the HS-DSCH is successfully received. High reliability is required when transmitting the ACK/NACK signal because the HARQ may be mistakenly performed due to erroneous ACK/NACK detection. For example, when the UE transmits the NACK signal but the BS recognizes it as the ACK signal, data may be lost.
In an FDD-based wireless communication system, the ACK/NACK signal is transmitted by using a high speed dedicated physical control channel (HS-DPCCH) which is a “dedicated physical control channel for HS-DSCH”. In most cases, the HS-DPCCH is used along with a dedicated channel (DCH) or an enhanced dedicated channel (E-DCH) instead of being used alone. Since high power is generally allocated to the DCH or the E-DCH, transmit power for the HS-DPCCH is decreased by an amount of the power allocated to the DCH or the E-DCH. Therefore, the reception performance of the BS may be deteriorated. This problem can be solved by repeatedly transmitting the ACK/NACK signal because the HS-DPCCH is a dedicated channel.
In a TDD-based wireless communication system, the ACK/NACK signal is transmitted on the HS-SICH. The DCH or the E-DCH may also be used. Similarly to the FDD-based wireless communication system, high power is allocated to the DCH or the E-DCH in most cases. Thus, transmit power for the HS-SICH is decreased by an amount of the allocated power, which may lead to deterioration in reception performance of the BS. However, unlike the FDD-based wireless communication system, the HS-SICH is a common channel shared by a plurality of UEs. Thus, it is difficult to assign the HS-SICH to one UE several times for repetitive transmission such as in the HS-DPCCH.
Accordingly, there is a need for a method capable of improving reliability when the ACK/NACK signal is transmitted on the HS-SICH.